Following are excerpts from the report by the International Atomic Energy Agency, which also urged Iran to answer queries about possible military dimensions to its nuclear program.

* HIGHER-SCALE ENRICHMENT

In February Iran started producing small batches of 20 percent-enriched uranium with 164 centrifuges at its Natanz pilot plant.

By April it had installed and was preparing a second set of centrifuges to support the first, according to the IAEA report.

They are not yet connected or operational and are under IAEA surveillance.

Iran has told the agency it will continue transferring material in small amounts to the site for higher enrichment. It produced around 5.7 kg of 20 percent-enriched uranium by early April and will have another batch ready soon.

The production rate is about 100g a day according to a senior official familiar with the Iran investigation.

* SURVEILLANCE

The IAEA was able to enhance its surveillance measures at the site earlier this month, improving camera positions, putting material and equipment under seal and most importantly, carrying out inspections at short notice.

But under Iran’s safeguards agreement with the IAEA, the measures should have been in place before its enrichment work rose beyond the 3.5 percent suitable for civilian power plant fuel, to ensure there were no covert diversions into weapons.

Iran says it needs 20 percent-enriched uranium to be converted into fuel rods for a nuclear medicine reactor about to run out of its imported supply. But Iran lacks the know-how to make such fuel, raising Western suspicions about its motives.

* MAIN NATANZ PLANT

The report said Iran had slightly increased the number of centrifuges actively enriching uranium to 3,936 — the first expansion in around a year. It had marginally lowered the total number of installed machines to 8,528.

Analysts said the rise in the number of machines enriching was not very significant and that Iran appeared to be concentrating its efforts elsewhere — possibly in an undisclosed location.

Iran’s P-1 centrifuges, adapted from a smuggled 1970s European design, have been plagued by breakdowns caused by a rapid expansion of enrichment in 2007-2008, analysts say.

But Iran is testing an advanced, more durable model able to refine uranium two or three times faster, and says it intends to introduce the model for production in the near future.

The IAEA asked Iran for information last month after Tehran announced it had developed a “third generation” of centrifuges, the report said. The agency repeated requests for information on sites for manufacturing centrifuges, details on research and development in uranium enrichment, uranium mining and milling.

Iran has not provided the requested information.

* STOCKPILING OF LOW-ENRICHED URANIUM

Iran told inspectors that it had accumulated around 2.4 tons of low-enriched uranium (LEU), about 300 kg more than at the end of January.

That total is enough to fuel about two atomic bombs, if it were further enriched to 90 percent fissile purity.

* POSSIBLE MILITARY DIMENSIONS

Since 2005, the IAEA has been probing Western intelligence reports indicating Iran has coordinated efforts to process uranium, test explosives at high altitude and revamp a ballistic missile cone to make it suitable for a nuclear warhead.

IAEA chief Yukiya Amano did not go into as much detail on this topic as in his previous report but kept the most important line — that the IAEA is concerned about possible current bomb research — not just work in the past.

“The agency remains concerned about the possible existence in Iran of past or current undisclosed nuclear related activities, involving military related organizations, including activities related to the development of a nuclear payload for a missile. There are indications that certain of these activities may have continued beyond 2004.”

The report urged Iran to engage with the IAEA on the issues and allow it to visit relevant sites, have access to all relevant equipment and documentation, and be allowed to interview all relevant officials “without further delay.”

* SECOND ENRICHMENT SITE

Iran agreed in October to inspections at the Fordow enrichment plant, being built inside a mountain bunker, after keeping it secret from the IAEA for three years. The West was angry that Iran had broken anti-proliferation rules.

Iran aims to start the plant near Qom in 2011 but, according to the report, it has not answered all the IAEA’s questions about the site. Tehran says this would go beyond its safeguards agreement with the IAEA.

“The agency considers that the questions it has raised do not go beyond the safeguards agreement, and that the information requested is essential for the agency to verify the chronology and original purpose of (the site).”

It has asked Iran to submit complete design documentation. Iran said it would provide updates on the design “subsequently.”

“In the agency’s view, some of the required information is already available to Iran and should already have been included,” the report said.

The report said no centrifuges had been introduced at Fordow yet. Inspectors had been checking for signs of undeclared nuclear activity after finding a small amount of depleted uranium particles on site. However a recent swipes have turned up no traces.

The agency said that Iran had still not provided it with information about its selected venues for its announced new nuclear sites, even though it is obliged to do this under its safeguards agreement.

* OTHER WORK

Iran has told the agency it will start research work on producing fuel for the Tehran medical research reactor.

The senior official said details of the planned work would be only a first step in a long and complicated process if it is carried out.

Tehran also told the agency in January that it had started research work on producing uranium metal at a laboratory in Tehran. In a visit in April the agency noted that some of the equipment — an electrochemical cell — had been removed. There was no explanation.

* DRUMS

Iran has continued to prevent the IAEA from taking samples from 756 50-liter drums of what Tehran described as domestically made heavy water found by IAEA inspectors at the Isfahan uranium processing center in October. The samples would help the IAEA determine the nature and origin of the material. Iran has told inspectors such sampling is beyond their mandate, and is denying the IAEA access to its heavy water production plant.

(Reporting by Sylvia Westall; Editing by Jon Boyle)